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Dec. 20, 2010 -- Breastfeeding babies for longer than six months may give them a brain boost that lasts well into their school years, a new study suggests, and this benefit may be particularly important for boys.

The study, which was published Monday in the journal Pediatrics, found that 10-year-olds who were breastfed for longer than six months as infants scored higher on standardized math, reading, writing, and spelling tests than children who were breastfed for less than six months.

However, when researchers adjusted their findings to correct for other factors associated with breastfeeding that might also be influencing academic achievement, like the mother’s age, family income, and how often the children were read to at home, only breastfed boys continued to see an advantage.

Critics of the study, however, call its conclusions misleading and point out that it suffers from many of the same problems that have long plagued this area of research. Namely, that moms who breastfeed are typically older, have higher IQs, are wealthier, and are more educated than moms who don’t breastfeed.

That makes it difficult for researchers to determine whether breastfed kids do better on intelligence tests because they were breastfed or because they have greater socioeconomic advantages.

Boys May See a Bigger Benefit

“In actual fact, the benefits to boys of breastfeeding seem to be quite significant,” says the study’s author, Wendy H. Oddy, PhD, MPH, who is an associate professor at the Telethon Institute for Child Health Research, in Perth, Australia. “If they were breastfed for more than six months, they did much better in math, reading, writing, spelling, and all the subjects,” she says.

Researchers aren’t sure why boys may get bigger benefit from breastfeeding than girls, but one theory suggests that breastfeeding may improve speech clarity, particularly for boys, and better speech has been associated with improved reading ability.

Another theory is that breastfeeding may help boys, who normally lag in development behind girls, mature more quickly.

Or, experts say, hormonal differences might be at work.

Tracking the Impact of Breastfeeding

Oddy’s study has followed 2,868 children who were born in Australia in the early 1990s.

Her group measured standardized math, reading, writing, and spelling scores of the children in the study, who were 10 years old at the time.

When looking at boys and girls independently, the researchers found that predominant breastfeeding for 6 months or more was significantly associated with increased scores in math, reading, writing, and spelling for boys, but there was no effect found on test scores for girls for any subject.

“Maybe humans really do need all the fatty acids, nutrients, bioactive factors that they get from human milk,” Oddy says. “If you’re trying to help kids do the best that they can, in school and in life, why wouldn’t you breastfeed?”

Research Mixed

But other studies looking at the possible long-term advantages of breastfeeding on intelligence and academic achievement have found little or no association after they corrected for other factors that also contribute to a child’s intelligence, like mom’s IQ and education, family income, and how often children are stimulated at home through practices like reading books together.

According to Miao Jiang, PhD, a maternal and child health researcher at the University of North Carolina at Chapel Hill, a key problem with the Australian study is that when researchers asked parents for permission to link breastfeeding records to the child’s testing scores, many families opted out. The 980 who stayed in were generally from two-parent, higher-income families and were more likely to have older moms who breastfed longer than moms who didn’t participate in the study.

“Therefore, the higher academic achievement found in this sample may quite likely be due to the advantaged socio-economic status, not breastfeeding,” Jiang says.